Shape memory alloys (SMAs) have been used in many applications to deform objects for particular purposes. For example, US 2001/021290 discloses an omnidirectional flex-type shape memory alloy actuator for omnidirectional flexing of wire-like structures or capillary tubes when connected to driving elements. The actuator can be used for deforming optical fibers, for example.
WO 94/19051 discloses a spatially distributed SMA film, which can be used around a catheter tube, for example, in combination with a very large scale integrated circuit to achieve a bendable structure. Like the one discussed above, this design is also suitable for shaping (bending) tubular structures.
US 2011/041641 discloses a deformable robotic surface has a plurality of control points, a plurality of rigid connectors extending between the control points, and a covering extending over the plurality of control points. The control points are moveable relative to each other. Movement of the control points relative to each other causes a corresponding movement of the covering and a corresponding movement of the control point connectors. The document also discloses the use of deformable materials as a replacement for rigid connectors between the control points. However, even in such variation, the upwards and downwards movement of the surface is achieved using extendable tubes below the connector network and large control points. Such structure can potentially make versatile shapes of surfaces possible but results in a thick and complex structure.
U.S. Pat. No. 8,057,206 discloses a reconfigurable tooling surface relying on a similar principle with a plurality of actuators beneath a variable stiffness covering. The surface, when reshaped using the actuator columns in a soft state, can be used to facilitate a resin molding process in prototyping applications, for example. Like in US 2001/041641, the actuators are mechanical and have a very limited mechanical working range, which results in a complex structure with very tight constraints as regards possible shapes of the surface formed.
U.S. Pat. No. 6,474,065 takes another approach. It discloses a multijunction thermoelectric actuator utilizing a plurality of Peltier elements in connection with alternating strips of electrically conducting dissimilar materials in a grid configuration such that a sheet is formed. The sheet is deformable as a whole towards either one or another side thereof by applying electric power across the sheet, since one of the surfaces heats up and the other one cools down. Such structure has is very limited as concerns the potential shapes of the deformed surface.
U.S. Pat. No. 6,133,547 on the other hand discloses a unitary sheet of shape memory alloy and a distributed activation system comprising grid of heating elements for locally heating the SMA sheet. Such structure has also a relatively limited freedom of out-of-plane motion and suffers from creasing if bent to two orthogonal dimensions at one location.
In summary, the shape change structures discussed above are either specifically designed for bending tubular structures or, if capable of forming non-tubular surfaces with a desired topology, are very complex and/or limited in surface shape. They are therefore not well suitable for all applications, including prototyping and manufacturing, for example.
Currently, the most growing method in prototyping is 3D printing. This is a technology that uses a movable head, which extrudes molten plastic onto a sheet, in layers. These layers slowly build up after many thousands of passes, from bottom to top, to create a final prototype/product. This technology of 3D printing has many advantages. It is relatively cheap to use and to acquire. A 3D printer can print any object that you design and they also allow an engineer or designer the ability to manufacture their prototype product in house, which drastically improves final product launching by cutting time needed to go from manufacturer to them, eliminating the middle man. They can simply print out the product, hold it in their hands, decide on changes or if it is good, then proceed to get a real mold made which will produce the sellable product.
While 3D printing has many advantages it also has some disadvantages that are inherent to it's design. The major one is that it takes a very long time to print. Something as small as a computer mouse can take many hours for a decent quality print. For something as big as a car's bumper it can take many days up to even a week. Since a 3D printer is reliant upon stepper motors (for X, Y, and Z movement) and the cooling of the molten plastic before it can be printed on, it leaves a large flaw which will make it nearly impossible to speed up in the future. In other-words, 3D printing will most likely always be a slow process.
Another disadvantage of 3D printing is that it is not suitable for a final product. Even if sped up it can not compare in speed to an injection molding machine that can produce full made plastic parts in seconds. Injection molding is the major manufacturing method of plastic parts currently. It uses two or more pieces of metal which have an accurate image CNC (computer numerical control) carved in to them. These pieces of metal are put together and then molten plastic is forced into a mold formed by them. Once full of plastic, the mold is opened and the new plastic object is released.
Although the injection molding machine is super fast and accurate, it also has big disadvantages. Major disadvantage is that it is very costly. To have a small mold made can cost a few thousand euros or more. To have a car bumper mold made can cost over one million euros. These molds cannot be used for anything else besides the purpose the were made for either. Also, to have one of these molds made for a product can take several weeks or even months. Additionally, if the mold is incorrect, the entire mold needs to be redone, requiring even more money and time.
Thus, there is a need for novel shape change structures for prototyping and manufacturing applications, for example, to form a mold section with easily variable shape.
There is also a need for surface structures with more flexibly variable shape to be used in many other applications besides prototyping. There is a particular need for thin shape change structure.